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IDT I2C Bus Interface
I2C Bus Master Interface
79RC32438 User Reference Manual
15 - 10
November 4, 2002
Notes
I
2
C Bus Master Status Register
Figure 15.12 I
2
C Bus Master Status Register (I2CMS)
CMD
Description:
Command.
When a value is written into this field, the corresponding command is initiated on the
I
2
C bus. Completion of the command is signalled when the done (D) bit in the I2CMS register is set.
Initial Value:
0x0 (NOP)
Read Value:
Previous command
Write Effect:
Initiate command on I
2
C bus
D
Description:
Done.
This bit is set when the command written to the I2CMCMD register has been completed
and the remaining status bits in this register are valid. At the completion of each command except
stop, the I
2
C bus SCL signal is held in a low state. This bit is automatically cleared when a com-
mand is written to the I2CMCMD register.
Initial Value:
0x0
Read Value:
Status
Write Effect:
Read-only
NA
Description:
No Acknowledge.
At the completion of each data transfer initiated by the I
2
C bus master inter-
face, if there was a “no acknowledge” signal, this bit is set to one. If there was an “acknowledge”
signal, this bit is cleared to zero. The absence or presence of the acknowledge signal is recorded
in this bit whether the acknowledge signal comes from the I
2
C bus master interface or an external
slave. This bit is automatically cleared when a command is written to the I2CMCMD register.
Initial Value:
Undefined
Read Value:
Status
Write Effect:
Read-only
LA
Description:
Lost Arbitration.
Arbitration takes place during each byte transmitted by the I
2
C bus master inter-
face. If the I
2
C bus master interface transmits a HIGH level during a bit period while another mas-
ter transmits a LOW level, then the I
2
C bus master interface has lost arbitration. When this occurs,
this bit is set and the I
2
C bus master interface tri-states the SLC pin for the remainder of the byte
transfer. This bit is automatically cleared when a command is written to the I2CMCMD register.
Initial Value:
Undefined
Read Value:
Status
Write Effect:
Read-only
I2CMS
0
31
D
0
28
1
NA
1
LA
1
ERR
1